This invention relates to chairs and more particularly to chairs for assisting persons in rising from a sitting to a standing position.
Persons recovering from surgery, suffering from arthritis, or otherwise partially incapacitated are often incapable of lifting themselves from a sitting position without the assistance of another person. One of the solutions proposed for enabling these persons to rise out of a chair without the assistance of another is the provision of springs located underneath the seat of a chair to lift the occupant with the seat to at least a partially standing position.
Examples of typical devices proposed are shown in U.S. Pat. Nos. 974,769 and 1,025,915, both issued to Hoff. Both of these patents show chairs having a seat mounted on links which are biased upwardly by means of two heavy strong springs. These chairs suffer from the problem that the greatest spring force is exerted during the initial upward movement of the seat and the spring force quickly decreases as the seat moves upwardly.
Thus, the user may initially be propelled upward at a rate higher than desirable, and not be provided with the assistance required when the chair seat approaches the upper limit of its travel. In addition, the heavy springs require a great deal of force to place the seat in its lowermost position which proves difficult for a user in weakened condition.
U.S. Pat. No. 2,539,034 to Ruby discloses a chair similar to those disclosed by Hoff. The chair of Ruby uses a plurality of springs to tilt the chair seat upwardly. The number of springs which are used is dependent on the amount of weight which is desired to be lifted. This chair suffers from the same problems as those associated with the chairs of Hoff in that the greatest spring force is applied during the initial upward movement of the seat and the force quickly decreases as the seat rises. In addition, the chair cannot accept a wide weight range of users without changing the structure of the chair by adding or taking away springs.
U.S. Pat. No. 4,838,612 to Cross discloses an assist chair having a seat which is biased upwardly by helical torsion springs. The seat being held down by a latching mechanism until a person sits in the chair, at which time the latching mechanism may be released to propel the user up to a standing position. Like other prior art assist chairs, this chair requires that a strong spring be provided in order for the spring force to be sufficient to lift the user during the final part of the movement of the seat upwardly.
Thus, a need exists for an assist chair which forces the seat upward with a relatively strong force throughout the extent of its travel, and which does not use a spring force which is so strong as to make it difficult for a person in weakened condition to force the seat down to its lowest position. In addition, the lift mechanism of the chair should be designed to accommodate a wide weight range of users.